#include <stdio.h>

int main() {
	int x;
	scanf("%d", &x);
	int n;
	int s = 1;
	for (n = 2; n < x; n++) {
		if (x % n == 0) {
			s = 0;
			break;
		}
	}
	if (s == 1) {
		printf("yes");
	} else {
		printf("no");
	}
	return 0;
}